Datasheet

REV. A
AD7709
–28–
MICROCONTROLLER
V
CC
GND
REF OUT2
REF IN
10␮F
0.1␮F
V
DD
AIN1
AIN2
CS
DOUT
SCLK
DIN
GND
REFIN(+)
REFIN(–)
0.1␮F
REF OUT1
CLOCK
LATCH
DATA
4.7␮F
COM
C1 C2 C3
AD7709
AD421
BOOST
V
CC
LV
0.01␮F
1k⍀
1000pF
LOOP
POWER
10␮F
3.3V
1.25V
DN25D
0.01␮F
LOOP
RTN
COMP
DRIVE
VARIABLES
AIN3
AIN4
Figure 23. Smart Transmitter Employing the AD7709
Smart Transmitters
Smart transmitters are another key design-in area for the AD7709.
The ⌺-⌬ converter, single-supply operation, 3-wire interface
capabilities, and small package size are all of benefit in smart
transmitters. Here, the entire smart transmitter must operate
from the 4–20 mA loop. Tolerances in the loop mean that the
amount of current available to power the transmitter is as low
as
3.5 mA. Figure 23 shows a block diagram of a smart transmitter
that includes the AD7709.
Not shown in Figure 23 is the isolated power source required to
power the front end.